1. Field of the Invention
The invention is related to the field of magnetic disk drive systems and, in particular, to a seed layer for a heat spreader in a magnetic recording head. More particularly, a heat spreader layer grown on the seed layer has a well-oriented crystalline structure to improve the thermal conductivity of the heat spreader layer and to improve heat dissipating characteristics in the magnetic recording head.
2. Statement of the Problem
Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more magnetic recording heads (sometimes referred to as sliders) that include read elements and write elements. A suspension arm holds the recording head above a magnetic disk. When the magnetic disk rotates, an air flow generated by the rotation of the magnetic disk causes the air bearing surface (ABS) side of the recording head to fly at a particular height above the magnetic disk. The height depends on the shape of the ABS. As the recording head rides on the air bearing, an actuator moves an arm that is connected to the suspension arm to position the read element and the write element over selected tracks of the magnetic disk.
To read data from the magnetic disk, transitions on a track of the magnetic disk create magnetic fields. As the read element passes over the transitions, the magnetic fields of the transitions modulate the resistance of the read element. The change in resistance of the read element is detected by passing a sense current through the read element and then measuring the change in voltage across the read element. The resulting signal is used to recover the data encoded on the track of the magnetic disk.
In one scheme used to write data to the magnetic disk, the write element passes a magnetic flux through a first write pole and into the magnetic disk. The magnetic flux flows through a soft underlayer in the magnetic disk and returns to the write element through a second write pole. The magnetic flux creates a transition in the magnetic disk that is stored as a bit.
A typical magnetic recording head is fabricated on a substrate using the following layers. An undercoat, such as Al2O3, is first formed on the substrate. Typical substrates are made from an Alumina-Titanium Carbide composite (AlTiC) material. The layers for the read element are then formed on the undercoat, where the layers of the read element typically include a first shield layer, a first gap layer, the read element (e.g., a magnetoresistive (MR) read element), a second gap layer, and a second shield layer. The layers for the write element are then formed. The layers for the write element typically include a first write pole, a coil, a second write pole, and gap material or insulating material between the write poles. The layers of the write element are then covered with an overcoat, such as Al2O3. A structure such as this for a magnetic recording head is illustrated in FIG. 1.
In normal operation of a magnetic disk drive system, heat can affect the magnetic recording head. For instance, because the magnetic recording head is fabricated from different materials having different coefficients of thermal expansion, the pole tips of the write element may protrude toward or recess away from the magnetic disk, which can negatively affect the operation of the write element. To alleviate the effects of heat, magnetic recording heads may be fabricated with a heat spreader. The heat spreader (or heat spreader layer) may be formed in the undercoat between the substrate and the first shield using a metallic material having a high thermal conductivity. Some typical materials used for a heat spreader layer are Tungsten (W) or a NiFe alloy. The heat spreader helps to dissipate heat in the magnetic recording head.
One problem with using Tungsten (W) for a heat spreader is that it corrodes when it is exposed at the ABS of the magnetic recording head. Thus, a heat spreader formed from Tungsten (W) has to be patterned, which requires extra lithography, hard mask, and etching steps. Also, the areas where the heat spreader is removed needs to be filled with an insulating material which adds time and expense to the fabrication process.
Another material suggested to be used as a possible heat spreader is Aluminum Nitride (AlN). Aluminum Nitride as a material has high thermal conductivity much like W, but does not corrode as easily. Unfortunately, when Aluminum Nitride is grown on an AlTiC substrate or an amorphous Al2O3 undercoat, the thermal conductivity is reduced which makes Aluminum Nitride less effective as a heat spreader. As a result, Aluminum Nitride has not been effectively used in magnetic recording heads as a material for a heat spreader.